Cooling or heating an electric car’s cabin can prove a difficult task from an energy efficiency standpoint. To tackle this issue, MIT researchers and Ford have developed a “thermal battery” system that’s far more advanced than what car makers use today.
For example, a Tesla Model S driven by a NY Times reporter, John Broder, in February this year had issues with this exact same problem, as heating was one of the factors that drained the car’s battery significantly. Well, it was proven later than Broder used the Model S just like a regular gas car when he drove it, didn’t take energy efficiency into account much and several other Model S owners proved one can take the same road trip he did without depleting the battery. I even interviewed Elon Musk on technicalities after the scandal was over.
But the Model S or any of the future Tesla cars may not be the first to benefit from the new MIT/Ford heating/cooling system. Of course, Ford is thinking about implementing it into a future Focus EV, hence improving its image of an electric car maker in advance and the car itself later on (in about two years). Their project got a $2.7 million grant from ARPA-E.
The new thermal battery’s secret lies in the materials that it’s made of. They used materials that can store large amounts of coolant in a small volume. The same coolant will be able to cool and heat the car cabin.
As MIT’s own Technology Review describes it, the thermal battery works as follows:
In the system, water is pumped into a low-pressure container, evaporating and absorbing heat in the process. The water vapor is then exposed to an adsorbant—a material with microscopic pores that have an affinity for water molecules. This material pulls the vapor out of the container, keeping the pressure low so more water can be pumped in and evaporated. This evaporative cooling process can be used to cool off the passenger compartment.
As the material adsorbs water molecules, heat is released; it can be run through a radiator and dissipated into the atmosphere when the system is used for cooling, or it can be used to warm up the passenger compartment. The system requires very little electricity—just enough to run a small pump and fans to blow cool or warm air.
After the adsorbant is full of water, the system is able to recharge itself by heating the adsorbant to 200 degrees Celsius. The water would then vaporize, condense and return to a reservoir. However, this recharging takes a bit long – 4 hours, but that is about the same time a Focus EV takes to recharge its battery. Note: the Model S uses a 90 kW charging station, which gives 150 miles-worth of juice in about 30 mins.
Basically, the science behind what MIT and Ford are putting together is not new at all – it’s called “evaporative cooling” and it’s being used by African people to keep food cooler (see “pot-in-pot refrigerator“) and by you, when you take a bath on a sunny day to cool yourself.
The innovation comes from using advanced materials to do it and making the system small enough to fit in a car. MIT also says their researchers are playing with metal-organic frameworks (MOF) and graphene oxide to suit their purpose.